From 3d8318870289d7b6b08677fcd2da6ceb0b082f8c Mon Sep 17 00:00:00 2001
From: Christian Theune <ct@flyingcircus.io>
Date: Mon, 18 May 2015 08:38:49 +0200
Subject: Enable lazy/sparse allocation of generation symlinks: avoid creating
 new generations if a generation already exists.

Alternatively or additionally I propose a mode where only the *last* generation will be sparse.
---
 src/nix-env/profiles.cc | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

(limited to 'src/nix-env/profiles.cc')

diff --git a/src/nix-env/profiles.cc b/src/nix-env/profiles.cc
index d8eb0ef5269c..1691dc099f4c 100644
--- a/src/nix-env/profiles.cc
+++ b/src/nix-env/profiles.cc
@@ -80,7 +80,22 @@ Path createGeneration(Path profile, Path outPath)
        previous ones. */
     int dummy;
     Generations gens = findGenerations(profile, dummy);
-    unsigned int num = gens.size() > 0 ? gens.back().number : 0;
+
+    unsigned int num;
+    if (gens.size() > 0) {
+        /* Check existing generations whether they represent an
+           environment we already materialized before.  In that case:
+           avoid cluttering the system with additional symlinks. */
+        for (auto & gen : gens) {
+            if (readLink(gen.path) == outPath) {
+                return gen.path;
+            }
+        }
+
+        num = gens.back().number;
+    } else {
+        num = 0;
+    }
 
     /* Create the new generation.  Note that addPermRoot() blocks if
        the garbage collector is running to prevent the stuff we've
-- 
cgit 1.4.1